Superabrasive wheel for mirror finishing

ABSTRACT

A superabrasive wheel ( 100, 200 ) for mirror finishing comprises an annular base plate ( 120, 220 ) having an end surface ( 121, 221 ) and a plurality of superabrasive layers ( 110, 210 ), each having a peripheral end surface ( 111 ), arranged along the peripheral direction of the annular base plate ( 120, 220 ) at intervals from each other and fixed onto the end surface ( 121, 221 ) of the base plate ( 120, 220 ). Each of the plurality of superabrasive layers ( 110, 210 ) has a flat plate shape, and is so arranged that the peripheral end surface ( 111 ) is substantially parallel to the rotary shaft of the superabrasive wheel ( 100, 200 ). A surface ( 113 ) defined by the thickness of the flat plate shape of each of the plurality of superabrasive layers ( 110, 210 ) is fixed onto the end surface ( 121, 221 ) of the base plate ( 120,220 ). In the superabrasive layers ( 110, 210 ), superabrasive grains are bonded by a binder of a vitrified bond. In another superabrasive wheel ( 300, 400 ) for mirror finishing, each of a plurality of superabrasive layers ( 310, 410 ) has an angularly bent plate shape, and is so arranged that a peripheral end surface ( 311 ) is substantially parallel to the rotary shaft of the superabrasive wheel ( 300, 400 ).

TECHNICAL FIELD

[0001] The present invention generally relates to a superabrasive wheel,and more specifically, it relates to a superabrasive wheel for mirrorfinishing employed for mirror-finishing a hard brittle material such assilicon, glass, ceramics, ferrite, rock crystal, cemented carbide or thelike.

BACKGROUND ART

[0002] Recently, high-precision mirror finishing of a material isrequired following abrupt technical innovation such as high integrationof a semiconductor device or ultraprecision in working of ceramics,glass, ferrite or the like. Such mirror finishing is generally performedby grinding referred to as lapping. More specifically, free abrasivegrains mixed into a lapping solution are fed between a lapping surfaceplate and a workpiece and rubbed with each other while applying pressureto the lapping surface plate and the workpiece in this grinding, forgrinding the workpiece due to rolling and scratching actions of the freeabrasive grains and providing a highly precise mirror-finished surfaceon the workpiece. In this lapping, however, a large quantity of freeabrasive grains are consumed to result in a large quantity of mixture,referred to as sludge, of used freed abrasive grains, chips caused bycutting the workpiece and the lapping solution, disadvantageouslyleading to deterioration of the working environment and pollution.

[0003] Therefore, mirror finishing employing fixed fine superabrasivegrains is actively studied/developed as a method substitutable for theaforementioned grinding employing free abrasive grains. As such mirrorfinishing employing fixed fine superabrasive grains, well known ismachining with a resin bond superabrasive wheel elastically holdingsuperabrasive grains of several μm in mean grain size or ELID(electrolytic in-progress dressing) grinding of dressing a metal bondsuperabrasive wheel while electrolytically dissolving a bond materialfor grinding a material with the metal bond superabrasive wheel.

[0004] In the aforementioned machining employing a resin bondsuperabrasive wheel, however, the sharpness of a grindstone isdeteriorated due to the fine superabrasive grains, and the grindstone isso remarkably worn that the worked surface of a workpiece is readilychanged in shape or reduced in precision and the grindstone must befrequently trued and dressed.

[0005] In the aforementioned working method employing a metal bondsuperabrasive wheel, the rigidity of the metal bond material is so highthat superabrasive grains finer than those in the resin bondsuperabrasive wheel must be used for obtaining a mirror-finished statesubstantially identical to the worked surface of the workpiece obtainedby the machining employing the resin bond superabrasive wheel, to resultin further deterioration of the sharpness of the grindstone.

[0006] In order to solve the problem of sharpness, a vitrified bond maybe used as the binder while reducing the area of a superabrasive layer.For example, a number of grooves may be formed in a superabrasive layeremploying a vitrified bond as the binder, so that superabrasive layerscontributing to grinding are formed at intervals from each other. Whenemploying a superabrasive wheel formed with such superabrasive layers,not only the conventional grinding employing free abrasive grains can bechanged to grinding employing fixed superabrasive grains but also avitrified bond superabrasive wheel for mirror finishing havingremarkably excellent sharpness and a long life can be provided byperforming truing and dressing with a diamond rotary dresser(hereinafter referred to as an RD). This is because large-volume poresof the vitrified bond serve as chip pockets for smoothly dischargingchips and enabling highly efficient machining, so that the workpiece canbe mirror-finished with small surface roughness.

[0007] In the aforementioned vitrified bond superabrasive wheel formirror finishing, a plurality of segment superabrasive layers arearranged along the peripheral direction of an annular base plate atintervals from each other. Depending on the size or the shape of thesegments, however, superabrasive grains crushed or falling during mirrorfinishing or shavings may be caught between the superabrasive layers andthe workpiece, to cause scratches on the surface of the workpiece.Further, a long time is required for a step of removing such scratches.

[0008] For example, Japanese Patent No. 2976806 proposes a structure ofa segment grindstone. This segment grindstone is formed with segmentfixing grooves so that a plurality of abrasive layer segments areengaged in the segment fixing grooves respectively. When performinggrinding with the segment grindstone having such a structure, however,the segment fixing grooves are clogged with shavings, anddischargeability for such shavings is extremely deteriorated.

[0009] Japanese Patent Laying-Open No. 54-137789 (1979) proposes astructure of a segment type grindstone for surface grinding. In thesegment type grindstone disclosed in this gazette, superabrasive layersare formed by sintering superabrasive grains with a binder such as ametal bond or a resin bond. When arranging superabrasive layers of platesegments shown in FIG. 4 or FIG. 6 of this gazette along the peripheraldirection of an annular base plate at intervals from each other,grinding resistance is disadvantageously increased due to the metal bondor the resin bond employed as the binder, although dischargeability forshavings is improved. Therefore, sharpness is deteriorated in grindingand the superabrasive layers are readily displaced from the base plate.The superabrasive layers are frequently displaced as the quantity ofgrinding is increased, to result in scratches. Consequently, the life ofthe grindstone is disadvantageously reduced.

[0010] The aforementioned gazette further proposes a structure of asegment type grindstone for surface grinding formed by arranging segmenttips of cylindrically formed superabrasive layers along the peripheraldirection of an annular base plate at intervals from each other inFIG. 1. However, although such cylindrical superabrasive layers arehardly displaced from the base plate in grinding, the inner sides of thecylindrical superabrasive layers are readily clogged with shavings anddischargeability for such shavings is disadvantageously deteriorated.

[0011] Accordingly, an object of the present invention is, in order tosolve the aforementioned problems, to provide a superabrasive wheel formirror finishing improved in dischargeability for superabrasive grainscrushed or falling during mirror finishing or shavings to hardly causescratches, capable of performing efficient machining and also capable ofpreventing scratches caused by displacement of a segment superabrasivelayer by rendering the superabrasive layer hardly displaceable from abase plate.

DISCLOSURE OF THE INVENTION

[0012] According to a first aspect of the present invention, asuperabrasive wheel for mirror finishing, comprising an annular baseplate having an end surface and a plurality of superabrasive layers,each having a peripheral end surface, arranged along the peripheraldirection of this annular base plate at intervals from each other andfixed onto the end surface of the base plate has the followingcharacteristics: Each of the plurality of superabrasive layers has aflat plate shape, and is so arranged that the peripheral end surface issubstantially parallel to the rotary shaft of the superabrasive wheel. Asurface defined by the thickness of the flat plate shape of each of theplurality of superabrasive layers, i.e., a surface along the directionof the thickness of the flat plate shape is fixed onto the end surfaceof the base plate. Superabrasive grains are bonded by a binder of avitrified bond in the superabrasive layers.

[0013] In the superabrasive wheel having the aforementioned structure,the surface defined by the thickness is fixed onto the end surface ofthe base plate in each of the superabrasive layers having the flat plateshape, whereby sufficient clearances can be defined between thesuperabrasive layers and dischargeability for chips and shavings can beimproved.

[0014] Further, the peripheral end surface of each superabrasive layeris arranged to be substantially parallel to the rotary shaft of thesuperabrasive wheel so that the position of a working surface of eachsuperabrasive layer is kept substantially constant with respect to aworkpiece in in-feed grinding although the superabrasive layer may beworn as the grinding progresses, whereby a stable working mode can besustained. Therefore, the working surface of each superabrasive layercan be regularly brought into contact with the central portion of theworkpiece. Thus, the finished surface of the workpiece is flattened.

[0015] In particular, the superabrasive grains are bonded by the binderof the vitrified bond in the flat-shaped superabrasive layers of theaforementioned superabrasive wheel, whereby grinding resistance can bereduced during grinding. Therefore, the superabrasive layers can berendered hardly displaceable during grinding. Thus, the surface of theworkpiece can be prevented from scratches resulting from displacement ofthe superabrasive layers.

[0016] Also when the quantity of working is increased, the grindingresistance can be kept low. Thus, reduction of the life resulting fromdisplacement of the superabrasive layers can be prevented.

[0017] In the aforementioned superabrasive wheel for mirror finishingaccording to the first aspect, the superabrasive layers preferably haveworking surfaces substantially perpendicular to the rotary shaft of thesuperabrasive wheel, and the working area of the plurality ofsuperabrasive layers preferably has a ratio of at least 5% and not morethan 80% with respect to the area of a ring shape defined by a lineconnecting the outer peripheral edges of the plurality of superabrasivelayers with each other and a line connecting the inner peripheral edgesof the plurality of superabrasive layers with each other.

[0018] In the superabrasive wheel according to the present invention,each superabrasive layer is brought into the flat plate shape, therebyenabling control of reducing the area ratio of the working surface ofthe superabrasive layer and increasing the force acting on eachsuperabrasive grain with respect to such continuous type superabrasivelayers that integrated continuous superabrasive layers are formed on theend surface of the superabrasive wheel. Thus, grindability of thesuperabrasive wheel can be improved while an autogenous action of thesuperabrasive wheel can be smoothed. Assuming that the radial widths ofthe superabrasive layers having the flat plate shape are identical toeach other, the area of the working surfaces of the plurality ofsuperabrasive layers having a flat plate shape is preferably set to aratio within the range of 5 to 80% of the area of the continuous typesuperabrasive layers, more preferably set within the range of 10 to 50%.Thus, working pressure of 2 to 10 times with respect to the continuoustype superabrasive layers is applied to the working surface of eachsuperabrasive layer of the flat plate shape in the superabrasive wheelaccording to the present invention, and a state of excellent sharpnesscan be sustained.

[0019] In the superabrasive wheel for mirror finishing according to thefirst aspect of the present invention, the superabrasive layerspreferably contain superabrasive grains of at least 0.1 μm and not morethan 100 μm in mean grain size. Synthetic superabrasive grains for aresin bond are suitable as the contained superabrasive grains. Thesynthetic superabrasive grains for a resin bond, having highercrushability as compared with synthetic superabrasive grains for a metalbond or a saw blade, are particularly preferable since small inserts canbe formed on the forward ends of the superabrasive grains by truing anddressing with an RD.

[0020] As synthetic diamond superabrasive grains for a resin bond, RVMor RJK1 (trade name) by GE Superabrasives, IRM (trade name) by TomeiDiamond Kabushiki Kaisha or CDA (trade name) by De Beers can be applied.As the synthetic diamond superabrasive grains for a resin bond, BMP1(trade name) by GE Superabrasives or SBNB, SBNT or SBNF (trade name) byShowa Denko K.K. can be applied.

[0021] While an RD is most preferably employed for performing truing anddressing in consideration of efficiency and molding precision, it isalso possible to employ a metal bond grindstone or an electrodepositiongrindstone having a diamond grain size of about #30 (grain diameter: 650μm) with no dispersion in forward end height of diamond abrasive grains.

[0022] According to a second aspect of the present invention, asuperabrasive wheel for mirror finishing comprising an annular baseplate having an end surface and a plurality of superabrasive layers,each having a peripheral end surface, arranged along the peripheraldirection of the annular base plate at intervals from each other andfixed onto the end surface of the base plate has the followingcharacteristics: Each of the plurality of superabrasive layers has anangularly bent plate shape, and is so arranged that the peripheral endsurface is substantially parallel to the rotary shaft of thesuperabrasive wheel. A surface defined by the thickness of the plateshape of each of the plurality of superabrasive layers is fixed onto theend surface of the base plate.

[0023] In the superabrasive wheel having the aforementioned structure,the surface defined by the thickness of the plate shape of each of thesuperabrasive layers, i.e., the surface along the direction of thethickness of the plate shape is fixed onto the end surface of the baseplate similarly to the aforementioned superabrasive wheel according tothe first aspect, whereby sufficient clearances can be defined betweenthe plurality of superabrasive layers so that dischargeability forshavings and chips can be improved.

[0024] Further, each of the superabrasive layers is so arranged that theperipheral end surface is substantially parallel to the rotary shaft ofthe superabrasive wheel similarly to the aforementioned superabrasivewheel according to the first aspect, whereby the position of a workingsurface of each superabrasive layer remains substantially constant withrespect to a workpiece also when the superabrasive layer is worn asgrinding progresses in in-feed grinding, so that a stable working modecan be sustained. Therefore, the working surface of the superabrasivelayer can be regularly brought into contact with the central portion ofthe workpiece. Thus, the finished surface of the workpiece is flattened.

[0025] Particularly in the superabrasive wheel according to the secondaspect of the present invention, each of the plurality of superabrasivelayers has the angularly bent plate shape. The surface defined by thethickness of the angular plate shape is fixed onto the end surface ofthe base plate, i.e., the shape of the surface of the superabrasivelayer fixed to the end surface of the base plate is angular, wherebyeach superabrasive layer is strengthened against resistance in thevertical direction and the rotational direction of the superabrasivewheel applied to the superabrasive layer in grinding, to be hardlydisplaced from the end surface of the base plate. Thus, the surface ofthe workpiece can be prevented from scratches resulting fromdisplacement of the superabrasive layer.

[0026] In the superabrasive layers of the superabrasive wheel for mirrorfinishing according to the second aspect of the present invention,superabrasive grains are preferably bonded by a binder of a vitrifiedbond. The vitrified bond can reduce grinding resistance in grinding asthe binder, and hence the superabrasive layers can be rendered morehardly displaceable from the end surface of the base plate. Thus, thesurface of the workpiece can be more effectively prevented fromscratches resulting from displacement of the superabrasive layers.Further, the vitrified bond, acting to smooth an autogenous action ofthe superabrasive wheel as the binder, contributes to sustainment ofexcellent sharpness.

[0027] In the superabrasive layers of the superabrasive wheel for mirrorfinishing according to the second aspect of the present invention,superabrasive grains are preferably bonded by a binder of a resin bond.The resin bond, acting to smooth the autogenous action of thesuperabrasive wheel as the binder similarly to the aforementionedvitrified bond, contributes to sustainment of excellent sharpness.Further, the resin bond having an elastic action as the bindereffectively reduces the sizes of scratches formed on the surface of theworkpiece during grinding, thereby reducing surface roughness of theworkpiece.

[0028] In the superabrasive wheel for mirror finishing according to thesecond aspect of the present invention, each of the plurality ofsuperabrasive layers is preferably so arranged that an angularly bentportion is located on the inner peripheral side of superabrasive wheel.An open part opposite to the angularly bent and closed part is locatedon the outer peripheral side of the superabrasive wheel due to thisstructure, whereby shavings and chips caused during grinding can bereadily discharged from the open part. Thus, dischargeability forshavings can be improved.

[0029] Each of the plurality of superabrasive layers preferably has aplate shape bent in a V shape. When each superabrasive layer of theplate shape is bent in the V shape, the superabrasive layer isstrengthened against resistance in the vertical direction and therotational direction of the superabrasive wheel applied to eachsuperabrasive layer during grinding, to be more hardly displaceable fromthe end surface of the base plate. Therefore, it is possible to preventoccurrence of scratches resulting from displacement of the superabrasivelayer during grinding.

[0030] When each of the superabrasive layers has the plate shape bent inthe V shape, the apical angle of the V shape is preferably at least 30°and not more than 150°. The apical angle of the V shape is set to atleast 30°, in order to efficiently discharge shavings and chips duringgrinding. Further, the apical angle of the V shape is set to not morethan 150°, so that a grinding fluid can be efficiently fed to a groundsurface of the workpiece and the superabrasive layers are hardlydisplaceable from the end surface of the base plate against resistancein grinding. In order to improve these effects, the apical angle of theV shape is more preferably set to at least 45° and not more than 90°.

[0031] As to the size of each superabrasive layer having the plate shapebent in the V shape, the length of a single side of the V shape, thethickness of the plate shape forming the V shape and the height of theplate shape forming the V shape, i.e., the length along the direction ofthe rotary shaft of the superabrasive wheel are preferably set to 2 to20 mm, 0.5 to 5 mm and 3 to 10 mm respectively. More preferably, thelength of a single side forming the V shape, the thickness of the plateshape forming the V shape and the height of the plate shape forming theV shape are set to 3 to 15 mm, 1 to 3 mm and 3 to 10 mm respectively.Further, the superabrasive layers having the plate shape bent in the Vshape are preferably fixed onto the end surface of the base plate alongthe peripheral direction of the annular base plate at intervals of 0.5to 20 mm from each other, and the intervals are more preferably set to 1to 10 mm. The intervals between the superabrasive layers are preferablyproperly decided in response to grinding conditions and the type of theworkpiece.

[0032] In the superabrasive wheel for mirror finishing according to thesecond aspect of the present invention, each of the plurality ofsuperabrasive layers preferably has a plate shape bent to have a curvedsurface. In other words, a corner portion preferably has a radius ofcurvature in the bent shape of the superabrasive layer. When eachsuperabrasive layer has the plate shape bent to have a curved surface,the grinding fluid can be efficiently fed while shavings and chips canbe effectively discharged similarly to the case of the plate shape bentin the V shape, and the superabrasive layer is hardly displaceable fromthe end surface of the base plate against resistance in grinding. Thus,scratches resulting from displacement of the superabrasive layer can beprevented in grinding. A semicylindrical shape obtained by halving acylindrical shape, a U shape, a C shape or the like can be employed asthe plate shape bent to have a curved surface.

[0033] In the superabrasive wheel for mirror finishing according to thesecond aspect of the present invention, the superabrasive layerspreferably have working surfaces substantially perpendicular to therotary shaft of the superabrasive wheel, and the working area of theplurality of superabrasive layers preferably has a ratio of at least 5%and not more than 80% with respect to the area of a ring shape definedby a line connecting the outer peripheral edges of the plurality ofsuperabrasive layers with each other and a line connecting the innerperipheral edges of the plurality of superabrasive layers with eachother.

[0034] The shape of each superabrasive layer is brought into the plateshape thereby enabling control of reducing the area ratio of the workingsurface of the superabrasive layer and increasing the force acting oneach superabrasive grain with respect to such a continuous typesuperabrasive layer that a single integrated continuous superabrasivelayer is formed on the end surface of the superabrasive wheel, improvinggrindability and smoothing the autogenous action of the superabrasivewheel. Assuming that the radial lengths of the superabrasive layers areidentical to each other, the area of the working surfaces of theplurality of superabrasive layers is preferably set to 5 to 80% of thearea of the continuous type superabrasive layer, more preferably setwithin the range of 10 to 50%. Thus, working pressure of 2 to 10 timeswith respect to the continuous type superabrasive layer is applied tothe working surface of each superabrasive layer in the superabrasivewheel according to the present invention, and a state of excellentsharpness can be sustained.

[0035] In the superabrasive wheel for mirror finishing according to thesecond aspect of the present invention, the superabrasive layerspreferably contain superabrasive grains of at least 0.1 μm and not morethan 100 μm in mean grain size. When employing a vitrified bond or aresin bond as a binder for the superabrasive wheel according to thesecond aspect of the present invention, synthetic superabrasive grainsfor a resin bond are suitable as the contained superabrasive grains. Thesynthetic superabrasive grains for a resin bond, having highercrushability as compared with synthetic superabrasive grains for a metalbond or a saw blade, are particularly preferable since small inserts canbe formed on the forward ends of the superabrasive grains by truing anddressing with an RD.

[0036] As synthetic diamond superabrasive grains for a resin bond, RVMor RJK1 (trade name) by GE Superabrasives, IRM (trade name) by TomeiDiamond Kabushiki Kaisha or CDA (trade name) by De Beers can be applied.As the synthetic diamond superabrasive grains for a resin bond, BMP1(trade name) by GE Superabrasives or SBNB, SBNT or SBNF (trade name) byShowa Denko K.K. can be applied.

[0037] While an RD is most preferably employed for truing and dressingthe superabrasive wheel according to the present invention inconsideration of efficiency and molding precision, it is also possibleto employ a metal bond grindstone or an electrodeposition grindstonehaving a diamond grain size of about #30 (grain diameter: 650 μm) withno dispersion in forward end, height of diamond abrasive grains.

[0038] When employing the superabrasive wheel for mirror finishingaccording to the present invention for grinding, as hereinabovedescribed, it is possible to effectively prevent superabrasive grainscrushed or falling during grinding or shavings and chips from beingcaught between the superabrasive layers and the workpiece and causingscratches on the surface of the workpiece. Thus, dischargeability forsuperabrasive grains or shavings can be improved while the superabrasivelayers are hardly displaceable from the end surface of the base plateduring grinding, whereby scratches resulting from displacement of thesuperabrasive layers can also be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a plan view showing a superabrasive wheel according toan embodiment of the present invention.

[0040]FIG. 2 is a sectional end view of the superabrasive wheel takenalong the line II-II in FIG. 1.

[0041]FIG. 3 is a plan view of a superabrasive wheel according to asecond embodiment of the present invention.

[0042]FIG. 4 is a plan view of a superabrasive wheel according to athird embodiment of the present invention.

[0043]FIG. 5 is a side elevational view of the superabrasive wheel shownin FIG. 4.

[0044]FIG. 6 is a sectional end view of the superabrasive wheel takenalong the line VI-VI in FIG. 4.

[0045]FIG. 7 is a partially fragmented perspective view showing asuperabrasive layer portion of the superabrasive wheel shown in FIG. 4.

[0046]FIG. 8 is a plan view of a superabrasive wheel according to afourth embodiment of the present invention.

[0047]FIG. 9 is a side elevational view of the superabrasive wheel shownin FIG. 8.

[0048]FIG. 10 is a perspective view schematically showing in-feedgrinding.

[0049]FIG. 11 is a diagram showing the relation between the number ofworking times, a PV value (the maximum width of irregularity on a workedsurface of a workpiece, i.e., the maximum distance between a peak and avalley) of the workpiece and surface roughness Ra obtained as a resultof a grinding test in Example 3 of the present invention.

[0050]FIG. 12 is a diagram showing the relation between the number ofworking times and surface roughness of workpieces obtained as one ofresults of grinding tests in Examples 3, 5, 6 and 7 of the presentinvention.

[0051]FIG. 13 is a diagram showing the relation between the number ofworking times and grinding resistance obtained as one of results ofgrinding tests in Examples 3, 5, 6 and 7 of the present invention.

[0052]FIG. 14 is a plan view showing a conductive mold employed forforming an electrodeposition diamond layer in Example 7 of the presentinvention.

[0053]FIG. 15 is a side elevational view showing the conductive moldemployed for forming he electrodeposition diamond layer in Example 7 ofthe present invention.

[0054]FIG. 16 is a plan view showing a superabrasive wheel formedaccording to comparative example 1 of the present invention.

[0055]FIG. 17 is a diagram showing the relation between the number ofworking times, a PV value of a workpiece and surface roughness Raobtained as a result of a grinding test in comparative example 1 of thepresent invention.

[0056]FIG. 18 is a partially fragmented sectional view showing a baseplate provided with a hole for mounting a superabrasive layer on an endsurface of the base plate in comparative example 4 of the presentinvention.

[0057]FIG. 19 is a plan view of a superabrasive wheel formed accordingto comparative example 4 of the present invention

BEST MODE FOR CARRYING OUT THE INVENTION

[0058] (First Embodiment)

[0059] As shown in FIGS. 1 and 2, a superabrasive wheel 100 according toa first embodiment of the present invention is formed by a cup-shapedbase plate 120 made of an aluminum alloy or the like and a plurality offlat superabrasive layers 110 fixed onto a single end surface 121 of thebase plate 120 at intervals from each other along the peripheraldirection. Surfaces defining the thickness of the superabrasive layers110, i.e., surfaces 113 along the direction of the thickness are fixedto circumferential grooves of a prescribed width formed in the singleend surface 121 of the base plate 120. Each superabrasive layer 110 isfixed to the single end surface 121 of the base plate 120 so that aperipheral end surface 111 of the superabrasive layer 110 issubstantially parallel to the rotary shaft of the superabrasive wheel110 and the longitudinal direction of the superabrasive layer 110 isalong the radial direction of the superabrasive wheel 100. Eachsuperabrasive layer 110 has a working surface 112 substantiallyperpendicular to the rotary shaft of the superabrasive wheel 110. A hole122 for receiving the rotary shaft of the superabrasive wheel 100 isformed in the central portion of the base plate 120.

[0060] (Second Embodiment)

[0061] As shown in FIG. 3, a superabrasive wheel 200 according to asecond embodiment of the present invention is formed by a cup-shapedbase plate 220 made of an aluminum alloy or the like and a plurality offlat superabrasive layers 210 fixed onto a single end surface 221 of thebase plate 220 at intervals from each other along the peripheraldirection. The superabrasive wheel 200 according to the secondembodiment is different from the superabrasive wheel 100 shown in FIGS.1 and 2 in a point that each superabrasive layer 210 is fixed onto thesingle end surface 221 of the base plate 220 so that the longitudinaldirection of each superabrasive layer 210 of the superabrasive wheel 220is at an angle α with respect to the radial direction of thesuperabrasive wheel 200.

[0062] (Third Embodiment)

[0063] As shown in FIGS. 4 to 7, a superabrasive wheel 300 according toa third embodiment of the present invention is formed by a cup-shapedbase plate 320 made of an aluminum alloy or the like and a plurality ofsuperabrasive layers 310, having an angularly bent plate shape, fixedonto a single end surface 321 of the base plate 320 at intervals fromeach other along the peripheral direction. A surface 313 defined by thethickness of the plate shape of each superabrasive layer 310 is fixed toa circumferential groove of a prescribed width formed on the end surfaceof the base plate 320. Each superabrasive layer 310 is fixed onto thesingle end surface 321 of the base plate 320 so that a peripheral endsurface 311 of each superabrasive layer 310 is substantially parallel tothe rotary shaft of the superabrasive wheel 300 and a bent portion 314of each superabrasive layer 310 is located on the inner peripheral sideof the superabrasive wheel 300. In this embodiment, the superabrasivelayer 310, having a V shape as the angularly bent plate shape, is sofixed onto the single end surface 313 of the base plate 320 that anapical part 314 of the V shape is located on the inner peripheral sideof the superabrasive wheel 300.

[0064] (Fourth Embodiment)

[0065] As shown in FIGS. 8 and 9, a superabrasive wheel 400 according toa fourth embodiment of the present invention is formed by a cup-shapedbase plate 420 made of an aluminum alloy or the like and a plurality ofsuperabrasive layers 410, having an angularly bent plate shape, fixedonto a single end surface 421 of the base plate 420 at intervals fromeach other along the peripheral direction. In this embodiment, theangularly bent plate shape of the superabrasive layers 410 is a plateshape bent to have a curved surface, i.e., a shape provided with acorner potion having a radius of curvature, dissimilarly to thesuperabrasive wheel 300 shown in FIGS. 4 to 7.

[0066] In each of the aforementioned first and second embodiments (thesuperabrasive wheel 100 shown in FIGS. 1 and 2 and the superabrasivewheel 200 shown in FIG. 3), a vitrified bond is employed as a binder. Ineach of the aforementioned third and fourth embodiments (thesuperabrasive wheel 300 shown in FIGS. 4 to 7 and the superabrasivewheel 400 shown in FIGS. 8 and 9), a vitrified bond or a resin bond ispreferably employed while a metal bond or an electrodeposition bond maybe employed as the binder. Ceramics-based glass is preferably employedfor the vitrified bond, which is more preferably in a porous structure.Phenol-based resin is preferably employed for the resin bond, to which afiller is more preferably added.

[0067] In any embodiment of the superabrasive wheel according to thepresent invention, the superabrasive layers are preferably bonded to thesingle end surface of the base plate with a resin-based adhesive or bybrazing.

EXAMPLES

[0068] Superabrasive wheels according to Examples of the presentinvention and superabrasive wheels according to comparative exampleswere manufactured for performing a mirror finishing test with eachsuperabrasive wheel in an in-feed grinding system. As an evaluationmethod for the mirror finishing test, a discoidal workpiece ofsingle-crystalline silicon having a diameter of 100 mm was ground at adepth of cut (total depth of cut in roughing and finishing) of 35 μm,and this grinding was regarded as single working. Therefore, thequantity of single grinding was 274.9 mm³. This grinding was continuedfor making evaluation with surface roughness Ra of the workpiece afterworking and a PV value, i.e., the maximum value (the maximum distancebetween a peak and a valley) of irregularity on the surface afterworking. All of the following surface roughness Ra and PV values wereobtained after performing grinding five times.

[0069] As shown in FIG. 10, a superabrasive wheel 1 mounted on a rotaryshaft 2 rotates along arrow R1 and a workpiece 3 rotates along arrow R2,for performing in-feed grinding. Referring to FIG. 10, superabrasivelayers are fixed to the lower surface of the superabrasive wheel 1. Thesuperabrasive wheel 1 is so provided that the superabrasive layers comeinto contact with a ground surface 31 of the workpiece 3. Thus, grindingis so performed that the superabrasive layers of the superabrasive wheel1 regularly pass through a central portion 32 of the workpiece 3. Suchgrinding is referred to as the in-feed grinding system.

Example 1

[0070] A vitrified bond and diamond abrasive grains of #3000 in grainsize (abrasive grain diameter: 2 to 6 μm) were homogeneously mixed witheach other. This mixture was pressed at the room temperature andthereafter fired in a firing furnace at a temperature of 1100° C., forpreparing diamond layers as superabrasive layers having a flat plateshape. The length of one side of the section of the flat plate shape was4 mm, the thickness was 1 mm, and the height was 5 mm. Table 1 shows thecomposition of the vitrified bond. TABLE 1 SiO₂  62 weight % Al₂O₃  17weight % K₂O   9 weight % CaO   4 weight % B₂O₃   2 weight % Na₂O   2weight % Fe₂O₃ 0.5 weight % MgO 0.3 weight %

[0071] Circumferential grooves of 4.5 mm in width were formed on asingle end surface of a base plate of an aluminum alloy having an outerdiameter of 200 mm and a thickness of 32 mm at a depth of 1 mm. Theplurality of diamond layers obtained in the aforementioned manner werebonded to these grooves with an epoxy resin-based adhesive at intervalsof 2.5 mm from each other so that the longitudinal direction of theflat-shaped sections of the diamond layers was along the radialdirection of the base plate. Thus, a diamond wheel for mirror finishingshown in FIG. 1 was prepared.

[0072] The obtained diamond wheel was mounted on a vertical spindlerotary table surface grinder and subjected truing and dressing with adiamond rotary dresser, for thereafter performing mirror finishing ofsingle-crystalline silicon. Table 2 shows the mirror finishingconditions. TABLE 2 Wheel Size φ200-32T Workpiece Single-CrystallineSilicon Grinder Vertical Spindle Rotary Table Surface Grinder RotationalFrequency of Wheel 3230 min⁻¹ Peripheral Velocity of Wheel 33.8 m/sec.Total Depth of Cut in Roughing 30 μm Cutting Speed in Roughing 20 μm/minTotal Depth of Cut in Finishing  5 μm Cutting Speed in Finishing  5μm/min. Spark-Out 30 sec. Rotational Frequency of Workpiece 100 r.p.m.

[0073] Consequently, the diamond wheel was excellent in sharpness, andthe workpiece was in an excellent state with surface roughness Ra of0.015 μm, a PV value of 0.20 μm and a small number of scratches.

Example 2

[0074] A vitrified bond and diamond abrasive grains of #3000 in grainsize (abrasive grain diameter: 2 to 6 μm) were homogeneously mixed witheach other. This mixture was pressed at the room temperature andthereafter fired in a firing furnace at a temperature of 1100° C., forpreparing diamond layers having a flat plate shape. The length of oneside of the section of the flat plate shape was 4 mm, the thickness was1 mm, and the height was 5 mm.

[0075] Circumferential grooves of 4.5 mm in width and 1 mm in depth wereformed on a single end surface of a base plate of an aluminum alloyhaving an outer diameter of 200 mm and a thickness of 32 mm. Theplurality of diamond layers obtained in the aforementioned manner werebonded to these grooves with an epoxy resin-based adhesive at intervalsof 2.5 mm from each other so that the longitudinal direction of thesection of the flat plate shape of the diamond layers was at an angle aof 20° with respect to the radial direction of the base plate, i.e., theradial direction of a superabrasive wheel. Thus, a diamond wheel formirror finishing shown in FIG. 3 was prepared.

[0076] The obtained diamond wheel was mounted on a vertical spindlerotary table surface grinder and subjected to truing and dressing with adiamond rotary dresser, for thereafter performing mirror finishing ofsingle-crystalline silicon. The mirror finishing conditions were similarto those for Example 1.

[0077] Consequently, the diamond wheel was excellent in sharpness, andthe workpiece was in an excellent state with surface roughness Ra of0.015 μm, a PV value of 0.21 μm and a small number of scratches.

Example 3

[0078] A vitrified bond and diamond abrasive grains of #3000 in grainsize (abrasive grain diameter: 2 to 6 μm) were homogeneously mixed witheach other. This mixture was pressed at the room temperature andthereafter fired in a firing furnace at a temperature of 1100° C., forpreparing plate-shaped diamond layers having a V-shaped section. Thelength of one side of the V-shaped section was 4 mm, the thickness ofthe plate shape was 1 mm, the angle between two sides forming theV-shaped section was 90°, and the height of the diamond layers was 5 mm.

[0079] Circumferential grooves of 4.5 mm in width and 1 mm in depth wereformed on a single end surface of a base plate of an aluminum alloyhaving an outer diameter of 200 mm and a thickness of 32 mm. Theplurality of diamond layers obtained in the aforementioned manner werebonded to these grooves with an epoxy resin-based adhesive at intervalsof 1 mm from each other so that the apical portions of the V-shapedsections were directed to the radial direction of the inner peripheralside of the base plate. Thus, a diamond wheel for mirror finishing shownin FIG. 4 was prepared.

[0080] The obtained diamond wheel was mounted on a vertical spindlerotary table surface grinder and subjected to truing and dressing with adiamond rotary dresser, for thereafter performing mirror finishing ofsingle-crystalline silicon. The mirror finishing conditions were similarto those for Example 1.

[0081] Consequently, the diamond wheel was excellent in sharpness, andthe workpiece was in an excellent state with surface roughness Ra of0.015 μm, a PV value of 0.21 μm and a small number of scratches.

[0082] The PV value and surface roughness of the workpiece varying withthe number of working times were measured. FIG. 11 shows the results ofthe measurement. FIG. 12 shows the relation between the number ofworking times and the surface roughness of the workpiece, and FIG. 13shows the relation between the number of working times and grindingresistance. It is understood from FIGS. 11 and 12 that the surfaceroughness and the PV value of the workpiece remain at relatively smalllevels and change in a small range also when the number of working timesis increased. Further, it is understood from FIG. 13 that the grindingresistance is not much changed but kept at a small value also when thenumber of working times is increased. Therefore, the grinding resistancecan be maintained low also when the quantity of working is increased,whereby not only scratches resulting from displacement of superabrasivelayers can be prevented during grinding but the life of thesuperabrasive wheel can be increased.

Example 4

[0083] A vitrified bond and diamond abrasive grains of #3000 in grainsize (abrasive grain diameter: 2 to 6 μm) were homogeneously mixed witheach other. This mixture was pressed at the room temperature andthereafter fired in a firing furnace at a temperature of 1100° C., forpreparing diamond layers having a plate shape and a semi-ring-shaped(semi-cylindrical) section. The radius of the semi-ring-shaped sectionwas 4 mm, the thickness of the plate shape was 1 mm, and the height was5 mm.

[0084] Circumferential grooves of 4.5 mm in width and 1 mm in depth wereformed on a single end surface of a base plate of an aluminum alloyhaving an outer diameter of 200 mm and a thickness of 32 mm. Theplurality of diamond layers obtained in the aforementioned manner werebonded to these grooves with an epoxy resin-based adhesive at intervalsof 1 mm from each other so that bent portions of the semi-ring-shapedsections of the diamond layers were directed to the radial direction ofthe inner peripheral side of the base plate. Thus, a diamond wheel formirror finishing shown in FIG. 8 was prepared.

[0085] The obtained diamond wheel was mounted on a vertical spindlerotary table surface grinder and subjected to truing and dressing with adiamond rotary dresser, for thereafter performing mirror finishing ofsingle-crystalline silicon. The mirror finishing conditions were similarto those for Example 1.

[0086] Consequently, the diamond wheel was excellent in sharpness, andthe workpiece was in an excellent state with surface roughness Ra of0.018 μm, a PV value of 0.24 μm and a small number of scratches.

Example 5

[0087] A resin bond and diamond abrasive grains of #2400 in grain size(abrasive grain diameter: 4 to 8 μm) were homogeneously mixed with eachother. This mixture was pressed at a temperature of 200° C. forpreparing diamond layers having a plate shape and a V-shaped section.The length of one side of the V-shaped section was 4 mm, the thicknessof the plate shape was 1 mm, the angle between two sides forming theV-shaped section was 90°, and the height of the diamond layers was 5 mm.The resin bond was mainly composed of phenol resin.

[0088] Circumferential grooves of 4.5 mm in width and 1 mm in depth wereformed on a single end surface of a base plate of an aluminum alloyhaving an outer diameter of 200 mm and a thickness of 32 mm. Theplurality of diamond layers obtained in the aforementioned manner werebonded to these grooves with an epoxy resin-based adhesive at intervalsof 1 mm from each other so that the apical portions of the V-shapedsections of the diamond layers were directed to the radial direction ofthe inner peripheral side of the base plate. Thus, a diamond wheel formirror finishing shown in FIG. 4 was prepared.

[0089] The obtained diamond wheel was mounted on a vertical spindlerotary table surface grinder and subjected to truing and dressing with adiamond rotary dresser, for thereafter performing mirror finishing ofsingle-crystalline silicon. The mirror finishing conditions were similarto those for Example 1.

[0090] Consequently, the diamond wheel was excellent in sharpness, andthe workpiece was in an excellent state with surface roughness Ra of0.014 μm, a PV value of 0.18 μm and a small number of scratches.

[0091] The surface roughness and grinding resistance of the workpiecevarying with the number of working times were measured. FIG. 12 showsthe relation between the number of working times and the surfaceroughness of the workpiece, and FIG. 13 shows the relation between thenumber of working times and grinding resistance. It is understood fromFIG. 12 that the surface roughness of the workpiece remains at a smalllevel and changes in a small range also when the number of working timesis increased. Further, it is understood from FIG. 13 that change of thegrinding resistance is small also when the number of working times isincreased, although the grinding resistance is higher as compared withthe superabrasive wheel according to Example 3 employing the vitrifiedbond. Thus, it is understood that the superabrasive wheel according toExample 5 employing the resin bond, having higher grinding resistance ascompared with the superabrasive wheel according to Example 3 employingthe vitrified bond, exhibits an autogenous action similarly to thesuperabrasive wheel employing the vitrified bond, and is improved insharpness.

Example 6

[0092] A metal bond and diamond abrasive grains of #2400 in grain size(abrasive grain diameter: 4 to 8 μm) were homogeneously mixed with eachother. This mixture was pressed at the room temperature and thereaftersintered by hot pressing, thereby preparing diamond layers having aplate shape and a V-shaped section. The length of one side of theV-shaped section was 4 mm, the thickness of the plate shape was 1 mm,the angle between two sides forming the V-shaped section was 900, andthe height was 5 mm. The metal bond was prepared from a copper-tin-basedalloy.

[0093] Circumferential grooves of 4.5 mm in width and 1 mm in depth wereformed on a single end surface of.a base plate of an aluminum alloyhaving an outer diameter of 200 mm and a thickness of 32 mm. Theplurality of diamond layers obtained in the aforementioned manner werebonded to these grooves with an epoxy resin-based adhesive at intervalsof 1 mm from each other so that the apical portions of the V-shapedsections of the diamond layers were directed to the radial direction ofthe inner peripheral side of the base plate. Thus, a diamond wheel formirror finishing shown in FIG. 4 was prepared.

[0094] The obtained diamond wheel was mounted on a vertical spindlerotary table surface grinder and subjected to truing and dressing with adiamond rotary dresser, for thereafter performing mirror finishing ofsingle-crystalline silicon. The mirror finishing conditions were similarto those for Example 1.

[0095] Consequently, the workpiece was in an excellent state withsurface roughness Ra of 0.021 μm, a PV value of 0.24 μm and a smallnumber of scratches.

[0096] However, sharpness of this diamond wheel was inferior insustainability as compared with the superabrasive wheel according toExample 3 employing the vitrified bond or the superabrasive wheelaccording to Example 5 employing the resin bond, and furtherdeteriorated as the working was repeated. A number of gossans werecaused on the surface of the workpiece. The surface roughness andgrinding resistance of the workpiece varying with the number of workingtimes were measured. FIG. 12 shows the relation between the number ofworking times and the surface roughness of the workpiece, and FIG. 13shows the relation between the number of working times and grindingresistance. It is understood from FIGS. 12 and 13 that a superabrasivewheel employing a metal bond has no autogenous action but exhibits sucha phenomenon that the surface of the metal bond is exposed and surfaceroughness of the workpiece is reduced when superabrasive grains areworn, while the grinding resistance is increased, the sharpness isdeteriorated and gossans are caused on the surface of the workpiece.

Example 7

[0097] A number of conductive molds 4 shown in FIGS. 14 and 15 wereprepared for forming electrodeposition diamond layers by performingelectrodeposition on V-shaped slopes 41 of the conductive molds 4. Thedimensions L1, L2 and L3 of the molds 4 were 6 mm, 5 mm and 4 mmrespectively. V-shaped depressions were formed on the upper surfaces ofthe molds 4. The molds 4 were introduced into a nickel sulfamide bathfor fixing diamond abrasive grains of #2400 in grain size (abrasivegrain diameter: 4 to 8 μm) to the upper surfaces of the molds byelectrocasting, thereby forming diamond layers of 0.7 mm in thickness.Thereafter the diamond layers were separated from the molds forpreparing diamond layers having a plate shape and a V-shaped section.The length of one side of the V-shaped section was 4 mm, the thicknessof the plate shape was 1 mm, the angle between two sides forming theV-shaped section was 90°, and the height was 5 mm.

[0098] Circumferential grooves of 4.5 mm in width and 1 mm in depth wereformed on a single end surface of a base plate of an aluminum alloyhaving an outer diameter of 200 mm and a thickness of 32 mm. Theplurality of diamond layers obtained in the aforementioned manner werebonded to these grooves with an epoxy resin-based adhesive at intervalsof 1 mm from each other so that the apical portions of the V-shapedsections were directed to the radial direction of the inner peripheralside of the base plate. Thus, a diamond wheel shown in FIG. 4 wasprepared.

[0099] The obtained diamond wheel was mounted on a vertical spindlerotary table surface grinder and subjected to truing and dressing with adiamond rotary dresser, for thereafter performing mirror finishing ofsingle-crystalline silicon. The mirror finishing conditions were similarto those for Example 1.

[0100] Consequently, the workpiece was in an excellent state withsurface roughness Ra of 0.029 μm, a PV value of 0.32 μm and a smallnumber of scratches.

[0101] However, sharpness of this diamond wheel was inferior insustainability as compared with the superabrasive wheel according toExample 3 employing the vitrified bond or the superabrasive wheelaccording to Example 5 employing the resin bond, and furtherdeteriorated as the working was repeated. Further, gossans were causedon the surface of the workpiece as the quantity of working wasincreased, to result in a number of scratches. The surface roughness andgrinding resistance of the workpiece varying with the number of workingtimes were measured. FIG. 12 shows the relation between the number ofworking times and the surface roughness of the workpiece, and FIG. 13shows the relation between the number of working times and grindingresistance. It is understood from FIGS. 12 and 13 that superabrasivegrains are worn in a superabrasive wheel employing an electrodepositionbond, the superabrasive wheel has no autogenous action, and grindingresistance is increased as the number of working times is increased, todeteriorate the sharpness.

Comparative Example 1

[0102] A vitrified bond and diamond abrasive grains of #3000 in grainsize (abrasive grain diameter: 2 to 6 μm) were homogeneously mixed witheach other. This mixture was pressed at the room temperature andthereafter fired in a firing furnace at a temperature of 1100° C., forpreparing ring-shaped diamond layers of 200 mm in outer diameter and 3mm in width. Grooves (bottomed) of 1 mm in width were formed on workingsurfaces of the ring-shaped diamond layers at regular intervals todivide the working surfaces from the outer peripheral sides toward theinner peripheral sides, while setting the circumferential length ofsuperabrasive layers defined between the grooves to 3 mm.

[0103] The ring-shaped diamond layers were bonded to a single endsurface of a base plate of an aluminum alloy having an outer diameter of200 mm and a thickness of 32 mm with an epoxy resin-based adhesive.Thus, a diamond wheel shown in FIG. 16 was prepared.

[0104] As shown in FIG. 16, ring-shaped superabrasive layers 510 arefixed onto a single end surface 521 of a base plate 520 to have groovesof 1 mm in width. A hole 522 for receiving the rotary shaft of asuperabrasive wheel 500 is provided on the central portion of the baseplate 520.

[0105] The obtained diamond wheel was mounted on a vertical spindlerotary table surface grinder and subjected to truing and dressing with adiamond rotary dresser, for thereafter performing mirror finishing ofsingle-crystalline silicon. The mirror finishing conditions were similarto those for Example 1.

[0106] Consequently, the surface roughness Ra and the PV value of theworkpiece were 0.031 μm and 0.34 μm respectively and scratches wereconcentrically caused on the central portion of the workpiece, althoughthe diamond wheel was excellent in sharpness. The surface roughness andthe PV value of the workpiece varying with the number of working timeswere measured. FIG. 17 shows the results. It is understood from FIG. 17that the surface roughness Ra and the PV value of the workpieceremarkably vary with the number of working times and the values thereofare relatively large as compared with the superabrasive wheel accordingto Example 3.

[0107] A diamond wheel similar to the above was prepared bymanufacturing a plurality of segment diamond layers having arcs of 200mm in outer diameter, widths of 3 mm and peripheral lengths of 3 mm,arranging the same at regular intervals of 1 mm in the form of a ringand bonding the same to a single end surface of a base plate. Also whenthis diamond wheel was employed for mirror-finishing single-crystallinesilicon, results similar to the above were obtained.

Comparative Example 2

[0108] A resin bond and diamond abrasive grains of #2400 in grain size(abrasive grain diameter: 4 to 8 μm) were homogeneously mixed with eachother. This mixture was pressed at a temperature of 200° C., forpreparing diamond layers having a flat plate shape. The plurality ofdiamond layers having a flat plate shape similarly to those in Example 1were bonded to a single end surface of a base plate with a resin bondsimilar to that in Example 5 by a method similar to that in Example 1.Thus, a diamond wheel for mirror grinding shown in FIG. 1 was prepared.

[0109] The obtained diamond wheel was mounted on a vertical spindlerotary table surface grinder and subjected to truing and dressing with adiamond rotary dresser, for thereafter performing mirror finishing ofsingle-crystalline silicon. The mirror finishing conditions were similarto those for Example 1.

[0110] Consequently, the workpiece was in an excellent state withsurface roughness Ra of 0.013 μm, a PV value of 0.18 μm and a smallnumber of scratches, while a working load was increased as the number ofworking times was increased, and the superabrasive layers were displacedfrom the base plate in 14-th working. This resulted in scratches, andthe superabrasive wheel was unusable.

Comparative Example 3

[0111] A metal bond and diamond abrasive grains of #2400 in grain size(abrasive grain diameter: 4 to 8 μm) were homogeneously mixed with eachother. This mixture was pressed at the room temperature and thereaftersintered by hot pressing, for preparing diamond layers having a flatplate shape. The plurality of diamond layers having a flat plate shapesimilarly to those in Example 1 were bonded to a single end surface of abase plate with an epoxy resin-based adhesive with a metal bond similarto that in Example 6 by a method similar to that in Example 1. Thus, adiamond wheel for mirror finishing shown in FIG. 1 was prepared.

[0112] The obtained diamond wheel was mounted on a vertical spindlerotary table surface grinder and subjected to truing and dressing with adiamond rotary dresser, for thereafter performing mirror finishing ofsingle-crystalline silicon. The mirror finishing conditions were similarto those for Example 1.

[0113] Consequently, the workpiece was in an excellent state withsurface roughness Ra of 0.021 μm, a PV value of 0.23 μm and a smallnumber of scratches, while a working load was increased as the number ofworking times was increased, and the superabrasive layers were displacedfrom the base plate in eighth working. This resulted in scratches on theworkpiece, and the superabrasive wheel was unusable.

Comparative Example 4

[0114] A vitrified bond and diamond abrasive grains of #3000 in grainsize (abrasive grain diameter: 2 to 6 μm) were homogeneously mixed witheach other. This mixture was pressed at the room temperature andthereafter fired in a firing furnace at a temperature of 1100° C., forpreparing plate-shaped diamond layers having a V-shaped section. Thelength of one side of the V-shaped section was 4 mm, the thickness ofthe plate shape was 1 mm, the angle between two sides forming theV-shaped section was 900, and the height was 10 mm.

[0115] A base plate of an aluminum alloy having an outer diameter of 200mm and a thickness of 32 mm was employed. As shown in FIG. 18, holes 623of 6 mm in diameter were formed on a single end surface 621 of a baseplate 620 by a number suitable for receiving the diamond layers. Theaxes of these holes 623 are inclined toward the outer peripheral side ofthe diamond wheel at an angle of 450.

[0116] The plurality of plate-shaped diamond layers having a V-shapedsection were inserted in the holes 623 of 6 mm in diameter formed in thesingle end surface 621 of the base plate 620 respectively, and bondedwith an epoxy resin-based adhesive. Thus, a diamond wheel shown in FIG.19 was prepared. As shown in FIG. 19, each plate-shaped superabrasivelayer 610 having a V-shaped section is fixed onto the single end surface621 of the base plate 620, and has a peripheral end surface inclined bythe angle of 450 toward the outer peripheral side with respect to therotary shaft of the superabrasive wheel 620. A hole 622 for receivingthe rotary shaft of the superabrasive wheel 600 is formed on the centralportion of the base plate 620.

[0117] The obtained diamond wheel was mounted on a vertical spindlerotary table surface grinder and subjected to truing and dressing with adiamond rotary dresser, for thereafter performing mirror finishing ofsingle-crystalline silicon. The mirror finishing conditions were similarto those for Example 1.

[0118] Consequently, the diamond layers were partially chipped due topressure applied to the diamond wheel during grinding, although thediamond wheel was excellent in sharpness. The surface roughness Ra andthe PV value of the workpiece were 0.018 μm and 0.36 μm respectively,and scratches resulting from the chipped superabrasive layers wereobserved on the surface of the workpiece.

[0119] From the aforementioned results of Examples and comparativeexamples, it has been confirmed that the diamond wheel for mirrorfinishing according to Example of the present invention has a smallernumber of scratches caused on a workpiece, can obtain high-precisionsurface roughness and is excellent in dischargeability for shavings andchips as compared with the conventional diamond wheel or the diamondwheel according to comparative example.

[0120] The embodiments and Examples disclosed above are to be consideredillustrative in all points and not restrictive. The scope of the presentinvention is shown not by the aforementioned embodiments or Examples butby the scope of claim for patent, and intended to include allcorrections and modifications within the meaning and range equivalent tothe scope of claim for patent.

[0121] Industrial Availability

[0122] The superabrasive wheel according to the present invention issuitably employed for mirror-finishing a hard brittle material such assilicon, glass, ceramics, ferrite, rock crystal, cemented carbide or thelike.

1. A superabrasive wheel (100, 200) for mirror finishing comprising: anannular base plate (120, 220) having an end surface (121, 221); and aplurality of superabrasive layers (110, 210), each having a peripheralend surface (111), arranged along the peripheral direction of saidannular base plate (120, 220) at intervals from each other and fixedonto said end surface (121, 221) of said base plate (120, 220), whereineach of said plurality of superabrasive layers (110, 210) has a flatplate shape and is so arranged that said peripheral end surface (111) issubstantially parallel to the rotary shaft of said superabrasive wheel(100, 200), a surface (113) defined by the thickness of the flat plateshape of each of said plurality of superabrasive layers (110, 210) isfixed onto said end surface (121, 221) of said base plate (120, 220),and superabrasive grains are bonded by a binder of a vitrified bond insaid superabrasive layers (110, 210):
 2. The superabrasive wheel formirror finishing according to claim 1, wherein said superabrasive layers(110, 210) have working surfaces (112) substantially perpendicular tothe rotary shaft of said superabrasive wheel (100, 200) and the workingarea of said plurality of superabrasive layers (110, 210) has a ratio ofat least 5% and not more than 80% with respect to the area of a ringshape defined by a line connecting the outer peripheral edges of saidplurality of superabrasive layers (110, 210) with each other and a lineconnecting the inner peripheral edges of said plurality of superabrasivelayers (110, 210) with each other.
 3. The superabrasive wheel for mirrorfinishing according to claim 1, wherein said superabrasive layers (110,210) contain superabrasive grains of at least 0.1 μm and not more than100 μm in mean grain size.
 4. A superabrasive wheel (300, 400) formirror finishing comprising: an annular base plate (320, 420) having anend surface (321, 421); and a plurality of superabrasive layers (310,410), each having a peripheral end surface (311), arranged along theperipheral direction of said annular base plate (320, 420) at intervalsfrom each other and fixed onto said end surface (321, 421) of said baseplate (320, 420), wherein each of said plurality of superabrasive layers(310, 410) has an angularly bent plate shape, and is so arranged thatsaid peripheral end surface (311) is substantially parallel to therotary shaft of said superabrasive wheel (300, 400), and a surface (313)defined by the thickness of the plate shape of each of said plurality ofsuperabrasive layers (310, 410) is fixed onto said end surface (321,421) of said base plate (320, 420).
 5. The superabrasive wheel formirror finishing according to claim 4, wherein superabrasive grains arebonded by a binder of a vitrified bond in said superabrasive layers(310, 410).
 6. The superabrasive wheel for mirror finishing according toclaim 4, wherein superabrasive grains are bonded by a binder of a resinbond in said superabrasive layers (310, 410).
 7. The superabrasive wheelfor mirror finishing according to claim 4, wherein each of saidplurality of superabrasive layers (310, 410) is so arranged that anangularly bent portion (314) is located on the inner peripheral side ofsaid superabrasive wheel (300, 400).
 8. The superabrasive wheel formirror finishing according to claim 4, wherein each of said plurality ofsuperabrasive layers (310) has a plate shape bent in a V shape.
 9. Thesuperabrasive wheel for mirror finishing according to claim 8, whereinthe apical angle of said V shape is at least 30° and not more than 150°.10. The superabrasive wheel for mirror finishing according to claim 4,wherein each of said plurality of superabrasive layers (410) has a plateshape bent to have a curved surface.
 11. The superabrasive wheel formirror finishing according to claim 4, wherein said superabrasive layers(310, 410) have working surfaces (312) substantially perpendicular tothe rotary shaft of said superabrasive wheel (300, 400), and the workingarea of said plurality of superabrasive layers (310, 410) has a ratio ofat least 5% and not more than 80% with respect to the area of a ringshape defined by a line connecting the outer peripheral edges of saidplurality of superabrasive layers (310, 410) with each other and a lineconnecting the inner peripheral edges of said plurality of superabrasivelayers (310, 410) with each other.
 12. The superabrasive wheel formirror finishing according to claim 4, wherein said superabrasive layers(310, 410) contain superabrasive grains of at least 0.1 μm and not morethan 100 μm in mean grain size.